Several nucleating agents for thermoplastic polymers are known in the art. These nucleating agents generally function by forming nuclei or providing sites for the formation and/or growth of crystals in the thermoplastic polymer as it solidifies from a molten state. The nuclei or sites provided by the nucleating agent allow the crystals to form within the cooling polymer at a higher temperature and/or at a more rapid rate than the crystals will form in the virgin, non-nucleated thermoplastic polymer. These effects can then permit processing of a nucleated thermoplastic polymer composition at cycle times that are shorter than the virgin, non-nucleated thermoplastic polymer. Nucleating agents can also be used to improve the physical properties (e.g., flexural modulus or optical clarity) of the thermoplastic polymer as compared to the virgin, non-nucleated thermoplastic polymer.
While there are many benefits associated with the use of nucleating agents in thermoplastics, there are some difficulties associated with their use. For example, many nucleating agents are insoluble materials that need to be evenly dispersed in the polymer in order to efficiently nucleate the polymer. However, it can be difficult to adequately disperse the nucleating agent in the polymer using the equipment available during the polymer manufacturing process. For example, many polymer manufacturing operations do not have dispersive mixing capabilities in their extrusion process that can adequately disperse a powdered nucleating in the manufactured polymer. Accordingly, resin manufacturers have resorted to the use of masterbatch compositions to incorporate nucleating agents, which is a procedure that can be costly and complex as discussed below.
A need therefore remains for an improved process for incorporating a nucleating agent into a polymer during the manufacture of the polymer and an additive composition suitable for use in such process. The process and additive composition described herein are believed to meet such need.